1. Field of the Invention
The present invention relates in general to a control system for a machine tool and more particularly, to an adaptive control apparatus for controlling the feed rate of a tool based on a machining load which acts on the tool during a machining operation.
2. Discussion of the Prior Art
In recent years, in order to machine a workpiece under an optimum condition, there has been used in a numerical control machine tool an adaptive control apparatus capable of controlling the feed rate of a cutting tool based on the variation in the load acting on the tool. In such an adaptive control apparatus, storage areas each for storing numerous load values sampled during a model machining operation are respectively provided for tools used therein, and the variation in the load during each model machining operation using a tool is sampled to be stored in one of the storage areas allocated to the tool. During an adaptive control machining operation, load values stored in the storage area allocated to the tool which is designated by a T-code included in a numerical control data block are successively read out, and the feed rate of the tool is controlled so that the load detected during the adaptive control machining operation follows the load value selectively read out from the storage area.
As aforementioned, in the prior art adaptive control apparatus, only one storage area is provided for one tool for storing load values sampled during a model machining operation. This disadvantageously makes it impossible to sample load values during a number of model machining operation wherein the same tool is used under different machining conditions, so as to perform adaptive control using an optimum one of the plural sampled data groups. The provision of only one storage are for one tool also disadvantageously makes it impossible to store plural groups of sampled data regarding the same cutting tool and then, to perform adaptive control machining operations on plural portions of a workpiece using the same tool based on the different sampled data groups.